JPH01159010A - Method and apparatus for holding screen/filter surface to clean state - Google Patents

Abstract

PURPOSE: To make it possible to exhibit a high suspension treating capability by providing the device with rotor blades moving with respect to a screen/filter surface in a suspension and forming a passage through which gas can flow by the rear end edges of the rotor blades. CONSTITUTION: The fluid (e.g. a fiber suspension) is introduced to the secondary side of the screen/filter surface 6. The pressure P1 of the fluid is so set as to be lower than the pressure P2 which is the total sum of the pressure of the suspension to be treated and the centrifugal force acting on the suspension and acts on the surface 6 but to be higher than the pressure P3 which is formed by the rear end edges of the rotor blades 9 moving with respect to the surface 6 on the machine surface, i.e., in the suspension or the area parts between the similar members. The surface 6 is made clear by regulating the stream of the inflow of the gas having the cleaning effect and forming the passages through which the gas can flow of only the area parts at the rear end edges of the blades 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for maintaining a screen or filter surface in a clean condition.

The device is suitable for use on perforated surfaces of equipment for processing fiber suspensions in the pulp and paper industry. Such surfaces sometimes tend to become clogged due to fibers entering and depositing in the openings in the screen/filter surface.

BACKGROUND OF THE INVENTION Fiber materials, particularly cellulose and wood fiber pulps, are processed as fiber suspensions. This fiber suspension becomes dense or coarse depending on the concentration of the suspension. Such pulps are processed, for example, by pumps, thickeners and various types of screens and filters. Parts of such means are intended to separate air from the fiber suspension, others to separate liquid from the fiber suspension, and still others to separate various fractions. and other parts are intended only to transport the fiber suspension. All means for carrying out the above-mentioned fractions are equipped with a perforated surface. In other words, it has a surface with holes and slots into which the fibers tend to enter and therefore the perforations tend to become clogged.

PRIOR TECHNOLOGY AND ITS PROBLEMS Previously known means involve mechanically wiping the perforation surface or rotating it in close proximity to the surface to apply a slight stroke pressure by the leading edge. The screen/filter surface is best kept clean by the rotor, which is designed to apply a small amount of pressure to the screen/filter surface, while also applying a slight stroke pressure in the opposite direction on the trailing edge area to create an underpressure area. It was maintained. This underpressure area is
It is primarily intended to loosen the fiber mat deposited on the screen/filter surface by creating turbulent flow conditions, such turbulence rupturing the fiber layer and thereby opening the perforations in that surface. Let it happen.

However, over long periods of operation, these openings become clogged with fibers, which cannot be relieved by the underpressure area formed by the rotor blades, but rather by the capacity of the screen/filter surface. gradually and continuously decreases, ie the pressure difference allowed across the screen becomes limited.

On the other hand, methods are known for cleaning filter surfaces by means of compressed air, for example with disc filters. The underpressure is strong in the bottom sector inside the filter disk, and this underpressure draws the fiber suspension against the filter surface, through which the liquid is filtered into the disk interior. As this disk is rotated and more fiber cake adheres to it from the pulp vat, a stream of compressed air is applied from the inside to the outside of the filter disk, which blows the pulp cake away from the filter surface. It is. Although this method is applicable to drum filters and screen filters, for example, it is not possible to maintain the screen/filter surface as clean as it should be; instead, the screen/filter surface is substantially A layer of fibers is deposited which reduces the functionality of the device and reduces its capacity.

OBJECTS OF THE INVENTION It is therefore an object of the invention to introduce a continuous flow of fiber suspension onto the screen/filter surface, such that this fiber suspension impedes the action of the screen/filter surface at any stage. An object of the present invention is to provide a method and apparatus that does not form a fiber mat on the screen/filter surface and allows the fiber suspension to flow along the surface toward an outlet opening while being effectively treated. .

A conventional device with a screen drum was used as the basis for the device in the example. The apparatus rotates a rotor close to the drum surface, which rotor may be in the form of a conventional blade member or the like.

The method of the present invention is characterized by the following features. That is, a fluid, either liquid or gas, is supplied downstream of the screen/filter surface, and the pressure P1 of the fluid is equal to both the pressure of the suspension being treated and the centrifugal force acting on the suspension. The pressure P exerted at the pressure and also on the screen/filter surface
2, formed in the area between said screen/filter surface and the trailing edge of a rotor blade or similar member which moves relative to the screen/filter surface in suspension. It is characterized by being higher than pressure P3. This is best achieved by regulating the flow of the cleaning gas and by ensuring that the only path through which the gas can flow is through the screen plate.

The surface to be cleaned follows the rotor blades and the area of that surface is determined by both the pressure fluctuations on the screen/filter surface and the gas flow rate used.

The device of the invention provides that the outer shell of the pulp processing device is provided with a conduit for the pressurized fluid, by means of which the space downstream of the screen/filter surface is pressurized. It is a feature.

An advantage obtained by the method and device of the invention is, for example, that it is ensured that the screen surface remains clean. The reason for this is that a large pressure difference can be utilized compared to previously known measures. By keeping the screen/filter surface clean, the pulping process becomes much more efficient compared to prior art equipment, resulting in significantly higher pulp throughput than previously possible. be.

The method and apparatus of the invention will be explained in greater detail below with reference to the accompanying drawings.

DESCRIPTION OF THE EMBODIMENTS According to FIG. 1, this pulp processing apparatus comprises an outer shell 1
, inlet conduit 2 for the pulp, outlet conduit 3 for the pulp. Exhaust conduit for accept or filtrate4. Conduit for compressed air or similar fluid5. It is composed of a screen drum 6 in a shell, and a rotorf equipped with a shaft 8 and a drive device. Preferably, the rotor 7 is arranged inside the screen drum so that the rotor blades 9 or similar elements are brought close to the surface of the screen drum 6. Preferably, the rotor blades 9 have the same shape as the blades of the screen device. This causes the leading edge of the rotor blade to apply a small pressure pulse against the screen drum, and the trailing edge of the blade to apply a small pressure pulse from the screen drum to the rotor.

As the method of the invention works (as shown in Figure 2), in the space for the accept/filtrate, i.e.
On the so-called secondary side, a pressure P1 is generated by the pulp, the centrifugal force 1 of the pulp and suspension, and the internal pressure, i.e. the so-called primary pressure P2 with respect to the screen surface, is directed towards the opposite side of the screen/filter surface. However, at the stage when underpressure (P3) is created by the rotor blade, the gas is exhausted from the area of the trailing edge of the blade through the screen/filter surface and this This ensures that the openings in the screen/filter surface are kept clean. In this way, the pressure relationship is P < P
Then, Pl>P3. After the effect of the rotor blades has ceased, both the centrifugal force and the pressure prevailing inside the screen overcome the gas pressure and the fiber suspension/liquid is filtered through the screen/filter surface as usual; The gas is moved to the center of the rotor. In this way, each blade with a trailing edge creates a backflow through the screen/filter surface, which flow clears the openings in the screen/filter surface. In other words, during one revolution of the rotor, the screen/filter surface receives as many cleaning streams as there are blades or similar elements on the rotor. Considering that modern screen surfaces are grooved in the direction of the rotor, each rotation of the rotor results in thousands of cleaning operations.

Typically, the rotating member of the device will be a screen/filter drum, allowing a stationary blade or similar member to generate the required pressure differential over the screen/filter surface. Gas or other similar fluids can also be supplied from a stationary pressurized space located close to the blades on the opposite side of the screen/filter surface.

At this stage, the gases entrained in the pulp and drawn through the screen/filter surfaces can be removed without causing major problems, for example by means of a centrifugal pump provided in the air separation system. , worth noting. Such centrifugal pumps are always needed for pulp conveyance. On the other hand, it should be noted that in a degassing system, the gas is mostly exhausted from the device.

As can be seen from the above description, a completely new method and apparatus has been developed which allows the screen/filter surface to be kept clean with high efficiency by preventing the build-up of fiber mats on the screen/filter surface. be. As is clear from the foregoing, the method and apparatus according to the invention can be successfully applied to a wide variety of pulp processing equipment. By increasing the pressure on the secondary side, backflow is effectively carried out over the entire area of the screen/filter drum, and this backflow can cause the screen/filter surface to become clogged, e.g. They can also be easily cleaned at the same time. In principle, the invention can be applied wherever clogging of perforated surfaces continues to be a problem and where compressed air or similar fluids can be considered for its cleaning. . If this is the case, the use of fluids for rinsing the screen/filter surface becomes valuable. Thus, the foregoing description does not limit the invention, but merely indicates certain preferred embodiments of the invention, and the scope of protection is defined in the claims. It is as described.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional pulp processing apparatus modified according to the requirements of the present invention. FIG. 2 is a detailed explanatory diagram for illustrating the functions of the screen. 1... Outer shell, 2... Inlet conduit,
3...Outlet conduit, 4...Discharge conduit, 5
...Compressed air conduit, 6...Screen drum, 7...Bowter, 8...Shaft, 9...Blade, 1o ······space.

Claims (3)

[Claims] (1) A method of maintaining a screen surface or filter surface in a clean state while processing a suspension of solid substances, the fluid being directed to the secondary side of the screen/filter surface, The pressure P_1 is the sum of the pressure of the suspension being treated and the centrifugal force acting on the suspension, and the pressure P_1 acting on the screen/filter surface.
2, formed in the area between said screen/filter surface and the trailing edge of a rotor blade or similar member which moves relative to the screen/filter surface in the element or suspension. A method for maintaining a screen/filter surface in a clean condition, characterized in that the pressure is higher than P_3. (2) The method according to claim 1, characterized in that the pressure P_1 is adjustable. (3) a device for keeping the screen/filter surface clean, including an outer shell (1), an inlet conduit for the pulp (2), conduits for at least two fractions (3, 4); and a pulp processing drum (6) disposed within the outer shell (1) and a screen/
Apparatus configured for connection to a pulp processing apparatus comprising a filter surface and an element, i.e. a rotor or similar element moving relative to the screen/filter surface, the outer shell (5) being connected to a pressurized fluid. characterized in that it comprises a conduit (5) for arranging and pressurizing a space (10) on the secondary side of the screen/filter surface by means of this conduit (5). screen/
A device that keeps the filter surface clean.